Added better navigation, some information

docs/system/dir.md

@@ -0,0 +1,4 @@
+*| [JavaECS](../README.md) | [docs](../overview.md) | system*
+# Overview
+### In this folder
+[system.md](./system.md)

docs/system/system.md

@@ -1,18 +1,28 @@
-*| [JavaECS](../../README.md) | [docs](../overview.md) | system*
+*| [JavaECS](../../README.md) | [docs](../overview.md) | [system](./dir.md) | system[]().md*
 # System
 
-### Contents
+### In this section
 [About](#About)
 
 [Implementation](#Implementation)
 
 [Examples](#Examples)
 
+[Notes](#Notes)
+
+
 ## About
 The system runs operations that must be performed on its assoiciated components.
 
 Typically, this is expected to be run every frame, though this is not a strict requirement.
 
+A system must implement the Runnable interface (this is a limited case of inheritence in this library)
+
+This allows a simpler implementation of any system, and also allows concurrency to be implemented with relative ease.
+
+
+
+
 Examples of the `system` include the `health_system`; which reads the value of the entitie's `health` component and ensures h > 0.
 ``` java
 void health_system(){
@@ -44,4 +54,9 @@ class SystemManager{
 
 ## Examples
 
+## Notes
+* Each system is represented by a name-index pair, and the action that gets executed every time the system is performed.    
+    * This is implicitly sequential, but a custom system that performs concurrent actions can be implemented.
+    * Care must be taken to ensure all threads are synchronised before the concurrent system finishes its execution
+